This is a 371 of PCT International Application No. PCT/EP97/07163, filed Dec. 19, 1997.
The invention relates to an ignition element, in particular for pyrotechnic mixtures.
Known EP 0 618 424 A1 is an ignition element which has two contact pins, between which a resistor element, for example a metal film element or an incandescing wire, is arranged. An ignition charge adjoins the resistor element. As soon as current is supplied to the contact pins, the ignition charge ignites because of the high temperature of the resistor element. Such ignition elements are used, for example, for igniting gas generators for use with air bags or safety belt tighteners.
Moreover, the ignition element has a carrier body. This is, for example, a plastics body, by means of which the external geometry of the ignition element is established and the individual components are protected. The carrier body of the ignition element is, for example, screwed or flanged in a holder of an air bag. For this purpose, the carrier body is introduced into the holder in such a way that the operating side, on which the ignition charge of the ignition element is arranged, is directed inwardly for example in the direction of a gas generator for inflating an air bag. In this way, the contact side, to which current can be supplied by way of the contact pins, is directed outwardly. To secure the ignition element a part of the holder is flanged around so that the ignition element is fixed in the holder and can no longer be pulled out in the direction of the contact side.
Both the flanging and the screwing of the ignition element in the holder are associated with high assembly expenditure because it must always be ensured that the ignition element is sealed tightly with the holder. Also, no gas is to be allowed to escape when there are high gas pressures on the operating side of the ignition element, these pressures occurring, for example, when an air bag is inflated. With flanged ignition elements leakages can occur because the flanging can be damaged due to the sudden great forces when the air bag is inflated.
An object of the invention is to create an ignition element which can be assembled in a holder quickly and easily.
The ignition element in accordance with the invention has a pyrotechnic ignition charge on the operating side of a carrier body and contacts on the contact side of the carrier body. Current is supplied to a resistor element by way of the contacts for the ignition of the ignition charge. The carrier body is held in the holder, for example of an air bag, a safety belt tightener or similar. For this purpose, in accordance with the invention, the carrier body has at least one integrally moulded stop spring which engages into a stop shoulder of the holder. For the assembly of the ignition element in the holder the carrier body is simply inserted into the holder until one or more stop springs engage into stop shoulders provided on the holder. The assembly of an ignition element in the holder is therefore simplified considerably. No costly operating steps such as flanging and no additional fastening elements such as screws are necessary.
The stop spring is preferably arranged on the operating side of the carrier body so that the stop spring additionally improves the seal between the ignition element and the holder.
In order to simplify the assembly capability, the stop shoulder is circumferential in the holder. A cylindrical carrier body can therefore be inserted into a likewise cylindrical holder in any rotational position. In this respect, the stop spring is preferably likewise circumferential so that it acts as a sealing lip. This further improves the seal between the carrier body of the ignition element and the holder.
In a preferred development of the ignition element the carrier body has a recess on the operating side in the region of the stop spring. After the ignition of the ignition charge by means of the supply of current to the contacts on the contact side of the carrier body, a pressure is produced on the operating side and therefore also in the recess, with the pressure pressing the stop spring against the inner surface of the holder. The bearing pressure between the stop spring and the holder is increased with increasing pressure on the operating side. An additional O-ring or another additional sealing can frequently be omitted owing to the seal which is guaranteed in this way. If the stop spring and the inner surface of the holder are formed in such a way that they abut each other in the unloaded state, an adequate seal is already guaranteed with little pressure.
In another preferred embodiment the inner dimensions of the holder in the region of the stop spring are smaller than the outer dimensions of the unloaded stop spring, with the result that the stop spring in the holder is prestressed. This further improves the seal.
To absorb the compressive forces arising during the ignition of the ignition charge, for example when an air bag is inflated, the holder has a steep shoulder which the carrier body abuts with the contact side. A displacement of the ignition element in the direction of the contact side is therefore prevented. The compressive forces therefore do not act on the stop spring and do not have to be absorbed by it. An impairing of the seal due to the gas pressure can therefore not occur in contrast to known ignition elements which are held in the holder by means of screwing or flanging around. Rather, the pressure on the operating side of the ignition element increases the seal between the latter and the holder because, when the pressure increases, the stop spring is pressed more greatly against the inner surface of the holder.